The present invention relates to a semiconductor device, and more particularly to a semiconductor device wherein a material for a metal electrode which can improve heat resistance is used.
Conventional semiconductor devices such as amorphous silicon solar cells and pin type photosensors are produced by (1) forming a transparent conductive thin film comprising ITO, ITO/SnO.sub.2, SnO.sub.2, In.sub.2 O.sub.3, Cd.sub.x SnO.sub.y (wherein x and y satisfy the relationships of 0.5.ltoreq.x.ltoreq.2 and 2.ltoreq.y.ltoreq.4, respectively), Ir.sub.z O.sub.1-z (wherein z satisfies the relationship of 0.33.ltoreq.z .ltoreq.0.5), and the like on a translucent substrate such as a glass and plastic film by means of sputtering method, electron beam vacuum deposition method, thermal CVD method, spray method, and the like, (2) forming an amorphous silicon layer having a pin structure on the transparent conductive thin film, and then (3) providing a metal electrode comprising, for example, Al, Ag, Ni, and the like by means of resistance heating vacuum deposition method, electron beam vacuum deposition method, and the like using a mask.
The conditions required for the above-mentioned metal electrode are as follows:
(1) To have a low electric resistance in spite of being a thin film.
(2) Not to form a potential barrier between a metal electrode and a semiconductor layer, and therefore to have a good ohmic property.
(3) To have a high adhesive strength to a semiconductor layer.
(4) To have a high reflectivity when a semiconductor device is a solar cell or a photosensor.
(5) To have a thermal stability and be hard to be diffused into a semiconductor layer.
These conditions have significant influences on the characteristics and lifetime of semiconductor devices.
As a material for conventional metal electrodes, there have been generally used Al, Ag, Ni, and the like. Among these materials, Al has superior properties in a single metal material with respect to the above items (1) to (4). However, Al has a drawback that it is apt to diffuse into the semiconductor at a high temperature in case that an amorphous silicon is employed as a semiconductor. Accordingly, in case that an Al electrode is exposed to a relatively high temperature when an amorphous semiconductor which might contain microcrystals and has an Al electrode is produced, or in case that the temperature rises during the use of a semiconductor device, Al is easily diffused into the semiconductor to lower the properties of the semiconductors. Therefore, the manufacturing process of semiconductor devices is extremely limited, or the lifetime of semiconductor is extremely shortened. For example, in case of employing Al as a backside electrode of an amorphous silicon solar cell which is placed in the outdoors, the temperature of the backside electrode rises up to about 80.degree. C. when it is irradiated by sunlight, whereby the performances of the solar cell are degraded.
The present invention was made to prevent the degradation of properties of semiconductor devices due to the diffusion of Al into the semicondcutor, of which diffusion is generated (1) when an Al electrode is exposed to a relatively high temperature during a manufacturing process after the Al electrode is formed, in case that a amorphous semiconductor which might contain microcrystal and has an Al electrode is produced, or (2) when the temperature rises during the use of a semiconductor device.